1. Field of the Invention
The present invention relates to the field of interlock mechanisms for an access door through which a cartridge containing a magnetic disc is inserted into a disc-drive assembly. The interlock prevents the access door from being opened, and thus the cartridge from being removed, during the time that a magnetic head is loaded onto the disc or in the process of being loaded.
2. Prior Art
After a cartridge containing a magnetic disc has been inserted into a disc-drive assembly through an access door, one or more magnetic heads are loaded onto the disc to record or reproduce information. The inadvertent removal of the disc from the disc-drive assembly while the magnetic heads are loaded onto the disc could result in accidental damage to the heads or the head flexures on which the heads are mounted or in damage to the oxide or other coating used for information storage. It is therefore desirable to interlock the access door with the carriage mechanism which moves the magnetic heads radially with respect to the disc or with the mechanism used to load the heads upon the disc so that the cartridge may not be removed from the disc-drive assembly unless the heads are removed from the cartridge or unloaded from the disc. However, in the event of a power failure or a malfunction within the disc-drive assembly, it is desirable that there be some means for manually unloading the magnetic heads from the disc and disabling the interlock so that the disc may safely be removed and inserted into a functioning disc-drive assembly.
Most commonly, an electrical interlock employing a solenoid latch and a switch for sensing whether the heads are loaded onto the disc or not is used to prevent the inadvertent opening of the access door while the heads are in the loaded condition. The disadvantage of the solenoid and switch approach is the high cost associated with the use of the solenoid and the switch. A second disadvantage is that in the event of a power failure, the manual activation of the mechanism in order to unload the heads from the disc and to unlatch the door is very difficult and usually requires an additional mechanism.
A mechanical approach for preventing the removal of a cartridge containing a magnetic disc from a read and write apparatus while magnetic heads are within the cartridge has been described in U.S. Pat. No. 3,797,033 issued to Prieur. The apparatuses described in that patent employ pivoting brackets which hold the cartridge in position when the carriage on which the magnetic heads ride is displaced so that the heads are within the cartridge.
In the embodiment shown in FIGS. 1 and 2 of the Prieur patent, the cartridge is prevented from being removed from the disc-drive apparatus by either a lug or a rod which prevents the the holding brackets from pivoting when the magnetic heads are within the cartridge. The lug or rod is attached to one end of a cable or pull wire, the other end of which is attached to a lever coupled to the carriage so that the lug or rod is pulled out of interference with the holding bracket when the carriage is retracted to withdraw the heads from the cartridge. According to the patent, this permits the safe removal of the cartridge. As stated by the inventor (column 4, lines 13 through 21), neither of the devices shown in FIGS. 1 or 2 of the Prieur patent permit the holding bracket to be manually unlocked to enable the cartridge to be removed and used in another apparatus in the event of a breakdown or power failure.
In FIG. 3 of the Prieur patent, another embodiment is shown in which the cartridge may be removed from the apparatus in the event of a breakdown. However, as noted in the patent (column 4, lines 36 through 39), the bracket is not locked. However, damage to the disc is allegedly prevented since whenever the bracket is rotated, the carriage is simultaneously displaced to retract the heads from the cartridge.